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By russell, September 9, 2009 10:17 am

When editing an image in Photoshop, it is very easy to run into the problem of digital image interpolation. You may be surprised how often interpolation occurs. Any time you resize (enlarge, compress, contract), resize, remap (rotate, flip), or resample an image, interpolation occurs.What is digital image interpolation?

Anytime you make an adjustment to an original image, the software has to guess where the pixels would normally be placed in that new changed (resized, flipped) image. Therefore, computer software has to make an estimation. And because the guess isn’t exact or fully accurate, the newly modified image instantly losses quality. The quality degradation is often untraceable to the eye, but it doesn’t mean that it’s not there!

However, if manipulation upon manipulation occurs (generations of changes), the result will soon be a poor quality image, and hence is considered destructive to the original image. When you make edits via the Levels Adjustment then this destruction will always occur.

These changes are permanent to the pixels and the missing information (the data the software had to “guess” upon), is completely gone.  If more and more of these destructive image adjustments occur, banding (also know as posterization) will take place. Banding can be described as when there is too little information spread too far apart and a rough transition between colors or tone develops. When banding occurs, it will become plainly visible to the eye and is especially apparent in print (or web) publications.

So, how can we avoid interpolation and create non-destructive image adjustments?

Adjustment Layers are the answer to non-destructively and safely manipulating images. By creating a New Adjustment Layer, you can avoid altering the original image information. The edits occur on a different layer, separated from the original image.  Plus, you can edit your adjustment at any time without losing all your past work.

By creating a layer mask, you will never truly alter the original image, because the layer mask is being applied to the individual adjustment, not the original photo.

Better yet, you can save your work to any adjustment you’ve made. The adjustment layer will not revert back to zero. It will stay the same using the latest information you’ve applied to it.

There are 12 adjustments (presets) that Photoshop offers:

•    Brightness/Contrast

•    Channel Mixer

•    Color Balance

•    Curves

•    Gradient Map

•    Hue/Saturation

•    Invert

•    Levels

•    Photo Filter•    Posterize

•    Selective Colors

•    ThresholdHaving flexibility in your photo editing is important. And learning to use adjustment layers is an important step in the process of becoming a professional Photoshop digital artist.